Synchronizing device for synchronous motors



June 18, 1940.

F'.'H. GULLIKSEN 2,205,253 SYNCHRONIZING DEVICE FOR SYNCX IRONOUS MOTORSOriginal Filed Nov. 13, 1934 /2 WITNESSES: INVENTOR 50 F77? H'Gu/MSen.BY PMWm ATTORNEY Patented June 18, 19.40.

PATENT OFFICE SYNCHRONIZING DEVICE FOR SYNOHBQ- NOUS MOTORS Finn H.Gulliksen, Wilki Westinghouse Electric pany, East PittsburghPennsylvania Application 11 Claims.

My invention relates to control systems for motors, and moreparticularlyto systems of control for controlling the starting sequence ofsynchronous motors.

One object of my invention is to provide for so controlling the startingoperation of a synchronous motor that the maximum pull-in torque issecured.

To better understand the broad object just mentioned, a brief statementof the problems involved in starting a synchronous motor may be verydesirable. Asynchronous motor, as such, has no starting torque andsynchronous motors are therefore usually started as induction motors.With the devices heretofore on the market a provision was made to excitethe field of the synchronous motor when the slip of the motor had beenreduced to a small value or, what amounts to the same thing, when themotor has attained some high per cent of synchronous speed. Variousmanually operable schemes and automatically operable schemes are on themarket.

In the automatic control systems, provision is made to energize thefield winding of the synchronous motor either a definite time after themotor has been energized or when themotor has attained some selected percent of synchronous speed. Also in some applications attempts are madeto energize the field winding of the synchronous motor not only at somespecified percentage of synchronous speed, but also with the correctpolarity. All of these devices, do not provide for a maximum pull-intorque, since the field is not excited at a time that has any definiterelation with reference to the phase of the alternating current suppliedto the synchronous motor. The synchronous motor therefore when energizedwith direct current, causes surges in the supply circuit, and causesother undesirable operating characteristics. Or, as is often the case, asynchronous motor may be operating a compressor in connection with whichmeans are provided to unload the motor during the starting cycle and toload the motor substantially simultaneously with the energization of thefield winding. If the time position of the rotor or field winding is notproperly selected with reference to the phase of the alternating currentsupplied to the motor, the motor may slip several poles or-even drop theload that was applied at the time the field was energized.

It is an object of my invention to energize the field winding of asynchronous motor at such a time, with reference to the phase of thealternsbnrg, Pa, assignor to & Manufacturing Com- Pa, a corporation ofNovember 13, 1934, Serial No. 752,825

Renewed May 8, 1939 nating current supplied to the motor that maximumpull-in torque is secured.

Another object of my invention is to energize the field winding of asynchronous motor during the starting cycle at a time having a definiterelation to a selected point on a wave of the alternating currentsupplied to the motor when the motor has attained a high per cent ofsynchronous speed.

A still further object of my invention is to energize the field windingof the synchronous motor with the correct polarity and at a time whensubstantially synchronous speed has been obtained by the motor, and at atime having a definite relation to the pole positions of the rotor withreference to the rotating field in the stator. Other objects andadvantages will become more apparent from a study of the followingspecification when considered in conjunction with the accompanyingdrawing-in which:

' Figure 1 is a diagrammatic showing of my 'invention, and

Fig. 2 shows somewhat graphically the pole position of the rotor withreference to a certain point on the curve showing the flux distributionof the rotating field in the stator.

Referring more particularly to Fig. 1, the reference character 93designates a synchronous motor which is adapted to be connected to busesl, 2 and 3 by the switches 8, 9 and iii. The synchronous motor II isprovided with a disc 34 which may be adjusted to have a definiterelation to the pole pieces of the rotor and which disc is provided witha plurality of slots 35, ,namely, one slot for each pair of poles of thesynchronous motor. These slots are uniformly distributed along a circleon the disc concentric with the shaft of the' synchronous motor and thedisc.

A second synchronous motor 26 is also adapted to be connected tothebuses i, 2 ad I by the switches 8, 9a'nd ll of the main linecontactor 99.

This synchronous motor is provided with a field winding 21 energizedfromv a suitable source 28 and may be a very small motor such as a clockmotor. The shaft of this synchronous motor 26 is provided with a disc 29similar to the disc 94. s

The disc 29 is designed to be adjustable on the shaft of the synchronousmotor 26 and is provided with a plurality of apertures 29 and IIdisposed 180 electrical degrees apart, and positioned on disc 29 atequal :distances from the shaft of motor 26 and arranged to cooperatewith the apertures 35.

A photocell 48 and a source of light 25 are so disposed with referenceto the discs." and It that light may fall on the photocell from thesource of light each time the phase of the alternating current and timeposition of the slots correspond. The grid 41 of suitable amplifier tube2| is interconnected with the photo-tube 48. The amplifier tube 2|therefore will be caused to break down each time the phase and timeposition of the slots correspond, namely, each time the photocell 48receives light from the source of light 25.

A glow tube 54 is adapted to be interconnected with the source ofalternating current and has a grid 55 which is controlled by theamplifier tube 2|. The circuit arrangement is such that the glow tube isenergized or will break down only during the time when the plate voltageis positive, provided the photocell obtains a light impulse during suchtime. It is therefore clear that by properly positioning the discs onthe shafts of the respective synchronous motors and providing propercontrol circuits any selected point on the positive portion of thealternating current waves supplied to the synchronous motors may beselected for the break down of the glow tube 54. The glow tube 54controls the energization of a field control relay 85 which, in turn,causes the energization of the field contactor 68 so that the fieldwinding 12 of the synchronous motor may be connected to the source ofdirect current power indicated by the buses 65 and 66 with the correctpolarity and at a time having a definite relation to a selected point onthe waves of alternating current supplied to the synchronous motor.

A better understanding of my invention can probably be had from a studyof the sequence of operation of the synchronous motor during a normalstarting cycle. Assuming that the attendant wishes to start thesynchronous motor 33, he depresses the starting switch 4 therebyestablishing a circuit from conductor 2 of the buses 2 and 3, throughthe switch 4, actuating coil 5 of the line contactor 99, stop switch 6,and conductor 1 to the bus 3. Energization of the coil 5 causes theoperation of the line contactor which closes the switches 8, 9 and I0,thereby energizing the conductors I2 and I3. Closure of the switch 9establishes a holding circuit for the line contactor which circuit maybe traced from the bus 2 through switch 9, conductor l4 and contactmembers 5 to the actuating coil 5.

The amplifier tube 2| is of the type requiring some time for the heatingof the cathode to a proper high temperature and in consequence thefilament 20 of the amplifier tube 2| is connected to be energizedimmediately upon the closing of the line contactor. The energization iseffected through the transformer l6 having its primary connected to thebuses l2 and I3 by the conductors I4 and I'I. The filament 20 isconnected to the secondary of the transformer IS, the filament 20,however, is not the cathode of the amplifier tube 2|, but merely heatsthe cathode 22 which is connected by a conductor intermediate a pair ofcondensers l8 and I9 connected across the secondary of the transformerit. The cathode 22 is thus connected at a neutral point with referenceto the alternating current and its negative bias is secured by anappropriate connection to a certain point of the control resistors 81 bya conductor 36.

Energization of conductors l2 and I3 causes the operation of thesynchronous motor 33 operating as an induction motor and also causes theOperation of the synchronous motor 25. Since the synchronous motor 26 isa small motor operating at substantially no load, it will readily pullinto synchronism, operating the disc 29 in synchronous relation to thealternating current supplied to the motor. The disc 34, however, beingconnected to the shaft of the motor 33, will operate at the same speedas the motor 33, namely at a slip with reference to the disc 23.

It will be noted that the source of light 25 is connected across theenergized conductors l4 and I! through the contact members, Hill of atiming means controlled by the main line contactor 35 and is thereforein operation, after a definite time, to energize the photocell 45 shouldthe apertures 3| and 35 be in the proper position, for instance, theposition shown in Fig. l. The time of closing of contact members I50 isso chosen that the motor 33 will be somewhere near synchronism when thelight 25 is energized.

A rectifier 31 is connected directly across the energized conductors l4and H, the direct current terminals of the rectifier 31 areinterconnected with a filter 33 which filters out any undesirableoscillations in the direct current whereby the conductors 35 and 40 aresupplied with a uniform direct current, the conductor 33 being positiveand the conductor 45 being negative. It should be noted that the cathode22 being connected intermediate the resistors 43 and 44 and near thejunction of the conductor 40 will have a negative bias. The anode 23 ofthe amplifier tube 2|, on the other hand, is connected through aresistor45 to the positive conductor 35. In other words,

the anode 23 and cathode 22 are connected across resistors 45, 4|, 42and 43. The auxiliary grid 24 is merely positioned about the anode 23 toselectively control the initial bias of the anode 23 with reference tothecathode 22.

The control grid 41 of the amplifier tube 2| is interconnected with thephoto-tube 45, the pair I of resistors 43 and 55 and a capacitor 5|. Itwill thus be apparent that the grid 41 will have its bias changed eachtime the light passes through the apertures 3| and 35 from the source oflight 25 onto the photocell 45. The current through amplifier tube 2|will thus be caused to increase each time the apertures in the two discscorrespond in position.

The glow tube 54, however, has its principal terminals, namely, theanode 53 and the cathode 56 connected to the conductors I4 and I1,respectively. The anode 53 is not connected directly to the conductorl4, but is connected in series circuit relation with the actuating coil52 of the field control relay 55. The cathode 56 is energized from asuitable source of current'as the battery 51. The control grid 55 on theother I hand is interconnected with the anode 23 of the amplifier tube2| through a capacitor 46, and is also interconnected with the negativeconductor 40 through a high resistance resistor 59.

The glow tube 54 will break down only if the increase in current of theamplifier tube has some definite relation to the-altemating currentwaves impressed upon the principal electrodes 53 and 55, respectively.

Referring to Fig. 2 of the drawing, if the wave 50 represents therotating field in the stator moving in the direction indicated by thearrow 3|, then the pole position of the rotor, namely the pole piece 13,may be indicated as moving in the direction of the arrow 52 but slippingwith reference to the rotating field. By a proper positioning of thediscs 29 and 34 and the coaction of the electrical system of controlprovided, any point on the wave may be selected for the break down timeof the glow tube 54. All points,

however, do not provide maximum pull-in torque but by appropriateadjustment of the discs 29 and the electric control system, taking intoaccount the time constants of the field control relay 6! and the fieldcontactor 66, and the polarity of the direct current in the buses 65 and66, a point on the wave 86 may be selected which will give maximumpull-in torque for the synchronous motor 33.

In the particular showing of Fig. 2, the point 63 is designated as thepoint of maximum pullin torque, but it is to be understood that thepoint is arbitrarily selected because the. time constants of the variousactuating units beyond the glow tube 54 may cause the point 63 to takeany other position, as for instance the point 64. The important featureis that any position on the wave can be selected, and once selected, themotor will always start in a predetermined manner and will automaticallypull into synchronism with a maximum pull-in torque.

If the photocell 48 is energized, namely, if the phase and time positionof the slots correspond, and the bias of the grid 55 has some desiredrelation with the changing potential of the anode 53 and cathode 56,then the glow tube 54 will become conducting. An energized circuit isthus established from the conductor l4 through the actuating coil 52,anode 53 and cathode 56, to the energized conductor ll. Energization ofthe coil 52 causes the operation of the field control relay 85 to closethe contact members 6| and 64. Closing of the contact members 6|establishes a circuit from the positive conductor 39 through conductor66. contact members 6|, actuating coil 62 and conductor 63 to thenegative conductor 40. The field control relay 85 thus remains energizedeven though they glow tube 54 becomes deenergized as the potential onthe principal electrodes I 53 and 56 changes.

Operation of the field control relay 85 establishes a circuit from thebus 66, contact members 64 and actuating coil 61 of the field contactor68 to the energized bus 65. Operation of the field contactor 68 causesthe closing of the contact members 69 and Ill and immediately thereafterthe opening of the contact members Ii. The field winding 12 is thusconnected directly to the direct current buses 65 and 66. The circuitfor the field winding may be traced from conductor 65 through contactmembers 69, conductor l3, field winding 12, conductor 16, field rheostatl6 and contact members to the energized conductor 66. The opening of thecontact members H immediately after the closing of the contact members69 and I0 removes the discharge.

circuit for the field winding 12 through the discharge resistor 15. Themovable contact portions of the contact members 66, I6 and II areresilient so that the field winding 12 is at no time on open circuitduring the operation of the field contactor 66. This is also true whenthe fieldcontactor 68 is deenergized, namely contact members 1| areclosed prior to the opening of contact members 69 and 10.

The conductors 65 and 66 will, of course, be either positive ornegative, but whichever polarity they do have is immaterial provided thediscs 29 and 34 are properly adjusted with reference'to the polarityselected for the conductors. The

discs may be adjusted at the manufacturers shops. The system of controlwill thus always automatically connect the field winding I2 to itssource of direct current with the correct polarity in addition toestablishing the circuit at a selected point on the alternating currentwave of the alternating current supplied to the synchronous motor.

From the foregoing explanations, it should be apparent that the fieldwinding is energized at a time when the rotor of the auxiliary timingmotor 26 has some definite position with reference to the position ofthe rotor of the motor 33. Or, in other words, the field switch 68completes its closing operation when a pole piece of a given polarity ofthe pole pieces for the field windings is in a given position withreference to a certain point on the curve showing the flux distributionof a given pole of the rotating field in the stator.

The subject matter hereinbefore disclosed is believed to be illustrativeof my invention because I am fully aware that others, particularly afterhaving had the benefit of the teachings of my invention, can readilydevise other circuit diagrams and systems of control for accomplishingthe novel results I have hereinbefore setforth, but I do not wish tobe'limited to the specific arrangement shown, but wish to be limitedonly by the appended claims and the pertinent prior art.

I claim as my invention:

1. A control system for a synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwindings wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source of direct current, switchingmeans adapted to connect the field windings to the source of directcurrent, control means comprising a glow tube having, an anode and acathode connected to said source of alternating current, and a controlelectrode, a-control electric discharge device operable a time intervalafter the armature is connected to the source of alternating current andconnected to vary the bias of the control electrode of said glow tube,means cooperable with said electric discharge device, for causing suchbias variation to take place each time the time position of a pole pieceand a phase of the alternating current corre spond, whereby saidglowttube will become conducting at a timewhen a pole piece of a certainpolarity has a definite position with reference to a given point ontherotating fiux wave of a given polarity produced by the armaturewindings, and means, operable when said glow-tube becomes conducting,adapted to cause the operation of said switching means.

2. A control system for a. synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwindings wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source of direct current, switchingmeans adapted to connect the field windings to the source of directcurrent, a relatively small auxiliary synchronous motor, having a statorand a rotor, adapted to be connected to the'source of alternatingcurrent at the same time the first named synchronous motor is connectedto said source of alternatingcurrent and designed to operate atsynchronous speed in a shorter time interval than the shorestaccelerating period of the first named synchronous motor, and switchingcontrol means responsive to a certain selected relative position of therotorsof said two motors for causing the operation of said switchingmeans;

3. A control system for a synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwindings wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source of direct current, switchingmeans adapted to connect the field windings to the source of directcurrent, a relatively small auxiliary synchronous motor, having a statorand a rotor, adapted to be connected to the source of alternatingcurrent at the same timethe first named synchronous motor is connectedto said source of alternating current and designed to operate atsynchronous speed in a shorter time interval than the shortestaccelerating period of the first named synchronous motor, switchingcontrol means responsive to a certain selected relative position of therotors of said two motors for causing the operation of said switching,means, and time-limit means adapted to delay the operation of saidswitching control means for a time after the armature windings of thefirst named motor are connected to said source of alternating current.

4. A control system for a synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwindings wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source of direct current, switchingmeans adapted to connect the field windings to the source of directcurrent, a relatively small auxiliary synchronous motor having a rotorand a stator and adapted to be connected to the source of alternatingcurrent at such a time that. it will be operating at synchronism beforethe per cent slip of the first named synchronous motor becomes small,photo-electric means adapted to be energized when the rotors of the twomotors have a certain selected relative position, and electronic means,controlled by said photo-electric means, adapted to control theoperation of said switching means.

5. A control system for a synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwindings wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source of direct current, switchingmeans adapted to connect the field windings to the source of directcurrent, a

relatively small auxiliary synchronous motor' having a rotor and astator and adapted to be connected to the source of alternating currentat such a time that it will be operating at synchronism before the percent slip of the first named synchronous motor becomes small,photoelectric means adapted to be energized when the rotors of the twomotors have a certain selected relative position, and time-limitelectronic means, controlled by said photo-electric means, adapted tocontrol the operation of said switchmg means.

6. A control system for a synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwindings wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source oi direct current, switchingmeans adapted to connect the fieldwindingstothelourceotdirectcm'rentarei tively small auxiliary motorconnected to the source of alternating current to be operable atsynchronism no later than at a time when the slip of the first mentionedsynchronous motor is at a certain low value, and switching control meansresponsive to a certain relative position of the rotors of the twomotors for causing the operation of said switching means.

7. A control system for a synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwindings wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source of direct current,

switching means adapted to connect the field windings to the source ofdirect current, a relatively small auxiliary motor connected to thesource of alternating current to be operable at synchronism no laterthan at a time when the slip of the first mentioned synchronous motor isat a certain low value, switching control means responsive to a certainrelative position of the rotors of the two motors, time-limit means fordelaying the time of eflective operation of said. switching controlmeans for an interval of time after the armature windings are connectedto said source of energy, and means responsive to the cooperative actionof said switching control means and said time-limit means to effect theoperation of said switching means.

8. A control system for a synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwindings wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source 01 direct,current, switchingmeans adapted to connect the field windings to the source of directcurrent, a relatively small auxiliary motor operating. at synchronismfrom said source of alternating current, a disc having apertures spaced180 electrical degrees apart mounted to be driven by the motor, a dischaving an aperture for each pair of poles of the first mentionedsynchronous motor mounted to be driven thereby, a photo-cell and asource of light so positioned with reference to said discs that thephoto-cell will be illuminated each time the phase and time position ofthe apertures correspond, and electronic means, controlled by theillumination oi the photo-cell, and

adapted to cause the operation of said switching switching means adaptedto connect the field windings to the source of direct current. arelatively small auxiliary motor operating at synchronism from saidsource of alternating current, a disc having apertures spaced 180electrical degrees apart mounted to be driven by the motor, a dischaving an aperture for each pair of poles of the first mentionedsynchronous motor mounted to be driven thereby, a photo-cell and asource oi light so positioned with rei'erenceto said discs that thephoto-cell will be illuminated each time the phase and time position ofthe apertures correspond, time-limit electronic means controlled by theillumination 0! the (I photo-cell, and a glow tube controlled by thetime-limit electronic means adapted to cause the operation of saidswitching means.

10. A control system for a synchronous motor, in combination, asynchronous motor having stator armature windings and rotor fieldwinding wound on pole pieces and starting windings, a source ofalternating current, means adapted to connect the armature windings tothe source of alternating current, a source of direct current, switchingmeans adapted to connect the field windings to the source of directcurrent, a relatively small auxiliary synchronous motor oper ating atsynchronism from the said source of alternating current, a disc havingapertures spaced 180 electrical degrees apart mounted on the shaft ofthe auxiliary motor, a disc having an aperture for each pair of poles ofthe first named synchronous motor mounted on the shaft of the firstnamed motor, a photocell and a source of light so positioned that thephoto-cell will be illuminated through the apertures each time a phaseand the time position of the apertures correspond, an electric dischargedevice adapted to be connected to the source of alternating current atthe same time the said armature windings are connected to the source andhaving a time constant whereby said electric discharge device does notbecome operative before the lapse of a certain time after connection tothe source, a discharge tube connected to the source of alternatingcurrent and controlled by said electric discharge device when operativewhereby said discharge tube becomes conducting at a certain point on onehalf of the-alternating currentv wave impressed on the tube, and means,operable when said discharge tube becomes conducting, to effect theoperation of said switching means. i

11. A control system for a synchronous motor,

in combination, a synchronous motor having stator armature windings androtor field windings wound on pole pieces and starting windings, asource of alternating current, means adapted to connect the armaturewindings to the source of alternating current, a source of directcurrent, switching means adapted -to connect the field windings to thesource of direct current, a relatively small auxiliary synchronous motoroperating at synchronism from the said source of alternating current, adisc having apertures spaced 180 electrical degrees apart mounted on theshaft of the auxiliary motor, a disc having an aperture for each pair ofpoles of the first named synchronous motor mounted on the shaft of thefirst named motor, a photo-cell and a source of light so positioned thatthe photo-cell will be illuminated through the apertures each time aphase and the time position of the apertures correspond, an electricdischarge device adapted to be connected to the source of alternatingcurrent at the same time the said armature windings are connected to thesource and having a time constant whereby said electric discharge devicedoes not become operative before the lapse of a certain time afterconnection to the source, a discharge tube connected to the source ofalternating current and controlled by said electric discharge devicewhen operative whereby said discharge tube becomes conducting atatcertain point on one half of the alternating current wave impressed onthe tube, means, operable when said discharge tube becomes conducting,to effect the operation of said switching means, and means for.selecting any point on one half of the alternating current waveimpressed on the discharge tube to make it conducting.

- FINN H. GUILIKSEN.

